If an exceptional incident occurs in a building, which incident can cause danger to the users of the building, it is important to enable a safe exit from the building for the users. This kind of serious exceptional incident can be e.g. a fire, an earthquake, a bomb threat or a similar type of event, which is of danger to the people in the building. An evacuation order can be given in the building, either for certain floors of the building or for the entire building, after detecting an exceptional incident. The transport systems located in the building, such as elevators, are in this case placed in an important role.
Generally the use of elevators in the event of fire can be prohibited. This is because a fire can damage an elevator system, in which case elevators are no longer safe to use for evacuating people to the exit floor of the building. It is also possible that the elevator stops working during an elevator run, in which case the elevator car may stop between floors leaving the elevator passengers trapped. Also the extinguishing water to be used for extinguishing fires may damage the electrical parts of the system e.g. by causing short-circuits in the electronics parts of the system.
Additionally in the event of a fire it is not sensible to direct the elevator car to, and then open the doors to, a floor on which the fire has progressed to an advanced stage. In this case the safety of the people already traveling in the elevator is endangered and the time needed for evacuation becomes longer, if it can be assumed that on this kind of floor there are no longer any people awaiting evacuation.
On the other hand, if the elevator system is constructed to be such that it withstands heat well or it is protected with suitable structures, the elevator system can very well be a feasible additional aid in the evacuation of the building. In high-rise buildings this is especially prominent, because the safe evacuation of a large number of people along the stairs and out of the building is extremely slow. If the elevators can be safely and reasonably controlled also during an emergency, the evacuation time can be substantially shortened. It follows from the above that travel of the elevators in emergencies must be controlled in accordance with a special evacuation state.
When an evacuation situation arises, one awkward point is receiving reliable information about the number of people to be evacuated on each floor. Additionally, if e.g. a destination call system is in use, in which each elevator user gives his/her personal destination information to the elevator system with a separate destination call panel instead of up-down pushbuttons, each person should separately give a destination call. In this case, after each destination call the group control optimizes the routing and allocates an elevator car to each person. If the number of people to be evacuated is considerable, the group control is significantly loaded and the route selections are not necessarily optimal from the viewpoint of evacuation.